\documentclass[letterpaper, 12pt]{article}
\usepackage{natbib}
\bibliographystyle{apa}
\bibliography{../resources/huge.bib}
\bibliography{../resources/local1.bib}
\bibliography{~/.vim/bundle/vimtex/test/tests/resources/local2.bib}
\bibliography{biblatex-examples.bib}
\begin{document}

Hello World.

\end{document}
